Variable geometry structures are used in the aerospace industry to alter the characteristics of a component depending on, for example, the operational mode of a gas turbine engine.
For example, UK Patent Application GB 2374121 discloses a gas turbine engine nozzle having a plurality of tabs which are movable between a deployed position and a non-deployed position. The tabs are formed from shape memory material. Below a predetermined temperature the tabs assume the non-deployed position. However, above the predetermined temperature, the shape memory material deforms to adopt the deployed position. Accordingly, the deployment of the tabs may be actuated by heating the tabs. In the deployed position the tabs interact with the gas stream to generate and shed noise-reducing vortices.
Whilst the shape memory material allows the geometry to be changed, the temperature must be maintained in order to retain the tabs in the deployed position. Furthermore, the mechanism typically only provides two different positions. That said, additional positions may be achieved using two-way shape memory or using zone heating, however this adds complexity to the structure and operation.
The present invention seeks to overcome the above mentioned problems and to provide a more adaptable structure.